Gate-tunable giant nonreciprocal charge transport in noncentrosymmetric oxide interfaces

Abstract

A polar conductor, where inversion symmetry is broken, may exhibit directional propagation of itinerant electrons, i.e., the rightward and leftward currents differ from each other, when time-reversal symmetry is also broken. This potential rectification effect was shown to be very weak due to the fact that the kinetic energy is much higher than the energies associated with symmetry breaking, producing weak perturbations. Here we demonstrate the appearance of giant nonreciprocal charge transport in the conductive oxide interface, LaAlO3/SrTiO3, where the electrons are confined to two-dimensions with low Fermi energy. In addition, the Rashba spin–orbit interaction correlated with the sub-band hierarchy of this system enables a strongly tunable nonreciprocal response by applying a gate voltage. The observed behavior of directional response in LaAlO3/SrTiO3 is associated with comparable energy scales among kinetic energy, spin–orbit interaction, and magnetic field, which inspires a promising route to enhance nonreciprocal response and its functionalities in spin orbitronics.

Nonreciprocal superconducting NbSe2 antenna

“…The normalized coefficient value which defined as and ( A here is the cross-sectional area of device) are 1.44 × 10 −11 T −1 A −1 m 2 and 7.55 × 10 −10 T −1 A −1 m 2 , respectively. Both are also higher than that observed in LaAlO 3 /SrTiO 3 oxide interface 11 (∼1.17 × 10 −11 T −1 A −1 m 2 ). The large enhancement of the nonreciprocity below the superconducting transition temperature is due to the reduction of the energy denominator from the Fermi energy (∼100 meV) to the superconducting gap (∼1 meV) 12 , 13 , 15 .…”

“…The maximum of γ and γ ′ are 6.53 × 10 2 T −1 A −1 and 3.43 × 10 4 T −1 A −1 , respectively. Both of them are higher than those reported in other non-superconducting systems such as Bi helix ( γ ∼ 10 −3 A −1 T −1 ) 34 , chiral organic materials ( γ ∼ 10 −2 A −1 T −1 ) 33 , BiTeBr ( γ ∼ 1 A −1 T −1 ) 10 and LaAlO 3 /SrTiO 3 oxide interface 11 ( γ ∼ 10 2 A −1 T −1 ). The normalized coefficient value which defined as and ( A here is the cross-sectional area of device) are 1.44 × 10 −11 T −1 A −1 m 2 and 7.55 × 10 −10 T −1 A −1 m 2 , respectively.…”

“…One particular example is the nonreciprocal charge transport in systems with both broken inversion and time-reversal symmetries 6 , where the electrical resistivity of a conductor is expected to vary depending on the current and magnetic field direction. Experimentally, nonreciprocal charge transport has been demonstrated in Bi helix 7 , chiral magnet 8 , 9 , Rashba semiconductor 10 , LaAlO 3 /SrTiO 3 oxide interface 11 and in various superconducting systems. These include superconducting non-centrosymmetric gated-MoS 2 12 , Bi 2 Te 3 /FeTe heterostructures 13 and MoGe/Y 3 Fe 5 O 12 bilayers 14 , where the nonreciprocal response is markedly enhanced by several orders of magnitude compared to non-superconducting systems due to the large energy scale difference between the Fermi energy and the superconducting gap 12 , 15 .…”

Nonreciprocal charge transport up to room temperature in bulk Rashba semiconductor α-GeTe

“…Under further breaking time inversion symmetry via applying a magnetic field B , nonreciprocal charge transport characterized by the current-direction I -dependent nonlinear resistivity can be expressed as 5 – 7 where R 0 , β , and γ are the resistance at zero magnetic field, the coefficient of the normal magnetoresistance, and the nonreciprocal coefficient, respectively. In this context, the nonreciprocal response scales linearly with both the applied electric current and the magnetic field, which has been recently discovered in polar semiconductors 6 , topological insulators (TIs) 8 , and several interface/surface Rashba systems 9 with spin-momentum locked bands. Unlike magnetoresistance in ferromagnet/heavy metals (FM/HMs) or FM/TI bilayers, in which the FM layer plays an essential role as a source of spin-dependent scattering, the nonreciprocal charge transport in noncentrosymmetric materials without FM layers introduces a new paradigm of unidirectional magnetoresistance (UMR) as a consequence of the second-order response to the electric field 10 – 14 .…”

“…Such a UMR sparks a surge of interest in realizing two-terminal rectification, memory, and logic devices 7 , 14 , 15 . To date, more efforts to hunt for the materials with larger γ values by taking the spin–orbit interaction and Fermi energy into account are being made in interface/surface Rashba systems 9 , 15 , 16 . However, given the low Rashba spin splitting energy, e.g., 3 meV (~35 k B ) in LaAlO 3 /SrTiO 3 9 , 5 meV (~58 k B ) in Ge(111) 15 , nonreciprocal transport can only be observed at very low temperature, and here γ -value decreases dramatically with increasing temperature due to the thermal fluctuation.…”